Remove unnecessary shutting down check in Scene.Heartbeat().  Add some method doc.  Rename HeartbeatThread, shuttingdown to conform to code standards.
Add a scene maintenance thread in parallel to the heartbeat thread.  The maintenance thread will end up running regular jobs that don't need to be in the main scene loop.

The idea is to make the critical main scene loop as skinny as possible - it doesn't need to run things that aren't time critical and don't depend on update ordering.
This will be done gradually over time to try and uncover any issues.  Many non-criticial scene loop activities are being launched on separate threadpool threads anyway.
This may also allow modules to register their own maintenance jobs without having to maintain their own timers and threads.
Currently the maintenance loop runs once a second, as opposed to the 89ms scene loop.
Add experimental SendPeriodicAppearanceUpdates = true/false setting to [Startup] in OpenSim.ini

On osgrid and other places, I have observed that manually sending appearance updates from the console often relieves grey avatar syndrome.
Despite hunting high and low, I haven't been able to find where this packet is sometimes being lost - it might be a persistent viewer bug for all I know.
Therefore, this experimental setting resends appearance data for everybody in the scene every 60 seconds.  These packets are small and the viewer only fetches texture
data if it doesn't already have it.
Default is false.
Add information about SendPeriodicAppearanceUpdates to OpenSimDefaults.ini for now.

Default remains false.
Comment out log message about sending periodic appearance updates.
fix yield prolog so it compiles with mono 2.11 there has been a bugzilla
report files with mono project in regards to this change, this simply
lets us move forward with using mono 2.11 for now :
https://bugzilla.xamarin.com/show_bug.cgi?id=4052
Have the PhysicsParameters module output console command responses
directly to the console rather than logging at INFO (which doesn't
output anything for WARN).

There should really be a WriteLine method on ICommandConsole so all
of the different commands don't have to figure out where the command
output should go.
BulletSim: Update list of TODO tasks
BulletSim: update BulletSim.dll to Bullet 2.80 and add libBulletSim.so to the new lib32 and lib64 binary directories
BulletSim: add some new runtime setable parameters to match the dll.
BulletSim: set buoyancy in only one place
BulletSim: Add AvatarRestitution parameter. Centralize computation of buoyancy for flying. Tweek avatar default friction and resititution
BulletSim: update TODO list. Rearrange code for readability. Add per object friction and restitution runtime settable parameters.
BulletSim: add updated (but not working) BulletSim dlls
BulletSim: remove confusion between angularVelocity and rotationalVelocity (there is still confusion in the rest of OpenSim). Enhance some debug statements to include the object ID.
BulletSim: add a bunch of internal Bullet configuration parameters to OpenSimDefaults.ini and the code.
BulletSim: Add new configuration parameters to get and set console commands
BulletSim: change default of shouldDisableContactPoolDynamicAllocation from False to True. It seems that collisions don't happen well when it is False (things fall through terrain).
Merge branch 'bulletsim1' of ssh://island.sciencesim.com/home/sceneapi/radams1/bs-opensim into bulletsim1

Conflicts:
	OpenSim/Region/Physics/BulletSPlugin/BSScene.cs
Give feedback when "terrain save-tile" is not successfully invoked.